New school hours are shown for students and parents outside of P.S. 230 in Brooklyn. Photo: Helayne Seidman

Along with their ABCs, city school kids will soon need to catch up on their Z’s.

Thanks to the new contract between the teachers union and Mayor de Blasio, some schools will be starting the day more than half an hour earlier in the fall — an unexpected change that furious parents say is already causing them to toss and turn.

“It’s really going to disrupt the morning schedule,” said mom Tara Pontani, whose 7-year-old twin boys attend PS 230 in Kensington, Brooklyn, where kids will have to show up next year at 8:20 a.m. instead of 8:40 a.m.

Pontani said the change came out of nowhere, and she and her husband will now have to scramble to adjust their schedules.

“This cuts down on family time in the morning,” she told The Post. “I don’t like that it wasn’t discussed with parents at all.”

Under the new $9 billion contract, a teacher’s day must end no later than 4 p.m. — but the agreement also calls for parent conferences and teacher training to replace 150 minutes a week of after-school tutoring. To fit in all the new requirements, some schools are starting and ending their day earlier.

“The sense that teacher development will fall on the backs of 5-year-old kids doesn’t make a lot of sense,” blasted dad Jon Powell of Carroll Gardens, whose 8-year-old daughter, Alex, attends PS 230.

“You are getting elementary-school kids who will have to be up at the crack of dawn — they’re being denied sleep at a very important developmental stage.”

“You are getting elementary-school kids who will have to be up at the crack of dawn — they’re being denied sleep at a very important developmental stage.”

“For people who work, that will mean more money on day-care coverage,” Powell noted.

Principals had been warning that school hours might change — but the Department of Education says the net result is the status quo.

“The instructional day for students and the total work time for teachers remains the same,” agency spokeswoman Devora Kaye said. “We encourage principals to work closely with their entire school community, including teachers, parents and administrators, to establish the parameters for how to best structure the school day to provide high-quality learning for all students.”

The city would not say which schools are now starting earlier. It was up to principals to decide on the amended dismissal and arrival times.

PS 230 initially set 8 a.m. as its new arrival time — and last week bowed to pressure and shifted it to 8:20 a.m., announcing the move on its Web site, even as a sign still hung outside its building announcing the 8 a.m. start time.

“Personally, I know our son doesn’t really ‘wake up’ mentally until 9 a.m., so this change in school hours will cost him nearly an hour of learning,” Timothy Edwards said in an online petition blasting the time change.